Certain methods of the kind mentioned at the outset are conventional. One example of the hybrid drive device described is designated as a “torque-split” hybrid. This stipulates a double drive having a first and a second drive train and an output-end drive used for driving the motor vehicle, one of the drive assemblies is able to be coupled with the first or the second drive train, and a further drive assembly being able to be connected, via a first clutch, to the first drive train and/or, via a second clutch, to the second drive train. This arrangement is of advantage, since the different drive assemblies are able to be driven using different rotational speeds, and thus each being able to be operated at optimal efficiency. An additional advantage is that no changes in the drive train of the motor vehicle, which is connected to the output-end drive of the hybrid drive device, have to be undertaken. Thus, the motor vehicle may be equipped first of all using a conventional drive, for instance, based on an internal combustion engine, and may later be converted to a hybrid drive device having at least two different drive assemblies. Because of the connection of the one drive assembly to the first or the second drive train, different transmissions ratios are able to be selected for the one drive assembly. That being the case, the latter may be operated in an optimal operating range and decoupled when necessary. From this, compared to the drive described in German Published Patent Application No. 199 03 936, the advantage comes about that the hybrid drive device is able to be implemented with two drive assemblies. This means that operating modes “boost”, “recuperation” and drive that is only possible with the one drive assembly are possible. In addition, no complex components are required, such as electrical components or planetary gears. However, the method described in the publication named, for operating a hybrid drive device of a motor vehicle, has the problem that switching over of the one drive assembly between the first and the second, or the second and the first drive train leads to a brief interruption of a drive torque or a deceleration torque, which has a negative effect on the comfort of the driver of the motor vehicle.